function fn() {
    let select = document.getElementsByClassName('select');
    console.log(select);
    for (let i = 0; i < select.length; i++) {
        if (select[i].checked === false) {
            select[i].checked = true
        } else {
            select[i].checked = false
        }
    }
}

function fn1() {
    let select = document.getElementsByClassName('select');
    console.log(select);
    for (let i = 0; i < select.length; i++) {
        select[i].checked = true
    }
}

function fn2() {
    let select = document.getElementsByClassName('select');
    console.log(select);
    for (let i = 0; i < select.length; i++) {
        select[i].checked = false
    }
}